It can be hard at times when everyone is tired (me included) and no one can sleep. My solution for this situation that doesn't include going crazy is to strap my children in the pram and go for a walk. Hooray for the endorphins of exercise, for not having screaming children hanging off me and for the possibility of them both falling asleep! It is also good to walk to a secondhand shop and find mags and good books!
Another thing that is good to do when you are a mother of small children (for me at least) is when they are finally in bed, don't tidy or catch up on cleaning. Just knit. It is relaxing and calming and after a day when it feels like you accomplished nothing, it lets you see progress and is inspiring for the next day.